A communications system can be seen as a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, data, multimedia and so on. The communications system may be circuit switched or packet switched. The communication system may be configured to provide wireless communication.
One example of a communications system is a cellular communications system. The coverage area of a cellular communications system is divided into cells. In general, user mobility is supported by re-routing connections (calls) to the transceiver network element corresponding to the cell where the user with his communications device is currently located. One example of a second generation cellular communications system is the Global System for Mobile telecommunications (GSM), and one example of a third generation cellular communications system is the Wideband CDMA (code division multiple access) system.
Traditionally, cellular communications systems have been circuit-switched systems. Some second generation cellular communications systems and many third generation cellular communication systems support both circuit-switched and packet-switched communications. The volume of packet-switched communications is increasing, so it is important to provide in cellular communications system capacity for transmitting packet-switched data.
One feature relating to packet-switched traffic is that this traffic is often asymmetric. As an example, consider a user browsing in the Internet. There is typically much more packet-switched traffic towards the user than in the opposite direction, that is, from the user towards a server in the Internet. Thus, in addition to supporting packet-switched data, there is need to support asymmetric packet-switched traffic in a communications system.
In the Wideband CDMA (WCDMA) system, one solution to support packet-switched traffic towards the communications devices is the High Speed Downlink Packet Access (HSDPA). HSDPA involves a new physical channel at the radio interface between the WCDMA system and a communications device. The HSDPA physical channel is shared by the communications devices using HSDPA. The HSDPA physical channel is separate from other WCDMA channels, and it increases the downlink packet-data transmission capacity of the WCDMA system at the radio interface.
The maximum data rate for the shared HSDPA channel is 10 Mbits per second. This data rate is about five times higher than data rates supported by other channels in the WCDMA system. As the transmission capacity at the radio interface increases, the transmission capacity within the WCDMA system needs to be also increased.
FIG. 1 shows schematically downlink packet data communications in a cellular communications system 100. A transceiver network element 110 providing communications over a radio interface to a communications device 101 is connected to a control network element 120. Several transceiver network elements are typically connected to one control network element. The control network element 120 is, in turn, connected to a core packet network 130 of the cellular communications system 100. In a WCDMA system, the transceiver network elements are called base stations or Node B's and the control network elements are called Radio Network Controllers.
The transceiver network element 110 is often connected to the control network element 120 by a fixed connection 112 provided by a transmission network 140. A transmission network provides fixed connections between endpoints. A fixed connection refers here to transmission capacity which is reserved for the specific connection independently of whether there is data to transmit over the connection. A fixed connection provided by a transmission network is also often called a leased line. The transmission network 140 may be implemented using, for example a plesiochronous digital hierarchy (PDH) or synchronous digital hierarchy (SDH). In a PDH transmission network, a common basic data transfer rate is 2,048 Mbit per second, and a fixed connection having this basic data transfer rate is called an E1 connection. For supporting speech connections to and from communications devices using the communications system 100, an E1 connection connecting the transceiver network element to the control network element, or vice versa, is generally divided in to 30×64 kbits/second channels plus 2×64 kbit/second channels for signaling and synchronization. It is alternatively possible to divide the capacity of an E1 connection, or the capacity of another type of leased line, between a number of connections/users in a different way.
To increase data transmission capacity between the control network element 120 and the transceiver network element 110 a common solution is to provide a plurality of leased line connections, for example a plurality of E1 connections. This may, however, prove not to be a feasible cost-effective solution for providing transmission capacity for the HSDPA downlink packet-data traffic, especially-if the maximum capacity for the HSDPA downlink data traffic is needed only occasionally.
It is appreciated that although the HSDPA and the WCDMA system as discussed above in detail, similar problems may arise in other communications systems.
Embodiments of the present invention aim to provide a feasible solution for providing data transmission capacity in a communications systems.